Research And Implementation Of High-precision Programmable AC Voltage Source

With the progress of science and technology and the development of precision electrical measurement technology,more and more electrical equipments puts more stringent requirements on the quality of power supply.Among them,high-quality AC standard power supply is indispensable in the power electronics industry,especially in research and development institutions,instrument verification,chip testing and other occasions.At present,these high-quality AC standard power supplies mainly rely on foreign imports.The output accuracy,output stability and load capacity of domestic AC power products is bad,and there is a certain gap compared with foreign products of the same type.Therefore,this paper designs a high-precision programmable AC voltage source,which enhances the competitiveness of localized products with its outstanding cost performance and has application promotion value.By comparing domestic and foreign AC voltage source products,in view of the shortages of domestic products,this paper proposes a solution,the solution mainly studies and analyzes the control circuit and power amplifier circuit of the AC voltage source system.In order to improve the quality of control,this paper designs a cascade control system.The control circuit consists of the main loop and the secondary loop of the cascade control system.The secondary loop centered on the P controller and the high-performance feedback network is mainly used to stabilize the output of the system.The main loop with STM32F415RGT6,high-precision AD converter,low-pass filter and DA converter as the core is mainly used to ensure the output accuracy of the system.Power amplifier circuit is one of the key points and difficulties of the whole design.In order to obtain sufficient circuit bandwidth and high transient response,this paper designs a class AB complementary symmetry power amplifier based on audio power amplifier device.In order to maximize the output signal of the control circuit,the power amplifier input stage circuit with the audio power amplifier LM3886 as the core is designed.Secondly,in order to ensure that the input signal is not distorted,a class AB power amplifier bias circuit based on triodes is designed.Then according to the characteristic curves of the audio power amplifier tubes and the requirements of the output current of the system,the upper and lower arms of the fully symmetrical power amplifier circuit are designed.Finally,for the range of system output voltage amplitude range,this design adopts multi-tap transformer boosting method to achieve a wide range of output voltage.In addition to the research on the whole system control circuit and power amplifier circuit,this thesis also deeply researches and analyzes the third generation frequency synthesis technology,and based on this technology,generates a sine wave signal to ensure the accuracy of the signal frequency.At the same time,the Qt human-computer interaction interface running on the Linux industrial tablet is designed to communicate with the AC voltage source via Ethernet.At the end of the paper,the output range(amplitude and frequency),the accuracy and stability of the output amplitude,the accuracy of the output frequency,the load capacity,the overload and short circuit protection functions of the AC voltage source prototype are tested.The results show that All indicators and functions meet the design requirements.